Test tube warmer



April 12, 1960 R. w. MARSTERS TEST TUBE WARMER Fild June 25, 1957 2Sheets-Sheet 1 INVENTOR. ROGER W; MARSTERS BY ATTORNEY April 12,

Filed June 1950 R. w. MARSTERS 2,932,718

TEST TUBE WARMER 25, 1957 2 Sheets-Sheet 2 F IG. 3

IISV

THERMOSTAT INVENTOR. ROGER W. MARSTERS B ATTORNEY United States Patent"2,932,718 TEST TUBE WARMER Roger W. Marsters, Cleveland, Ohio, asslgnorof three- Application June 25, 1957, Serial No. 667,794 3 Claims. (Cl.219-43) This invention pertains to the art of heating and moreparticularly to apparatus for heating liquids while contained inelongated cylindrical containers.

The invention is particularly applicable to the heating of bloodspecimens contained in glass test tubes to a predetermined temperatureand maintaining such specimens at this temperature for any desiredlength of time and will be described with particular reference thereto,although it will be appreciated that the invention has broaderapplications.

By test tubes, it is meant an elongated, cylindrical container closed atone end and open at the other, usually of glass but possibly of othermaterials such as metal into which liquids or solids are placed for thepurpose of conducting research, experiments or other laboratory tests.

It is normally necessary to raise the temperature of blood specimenswhile contained in test tubes to a temperature of approximately 37 C.for the purposes of conducting tests thereon. Heretofore, the specimenand its test tube had been heated either by placing the test tube in acirculated stream of warm air or by submerging the lower end in a heatedwater bath.

With the heated air, the difficulty has heretofore been that the timerequired to bring a specimen to a desired temperature has been undulylong. Thus certain tests indicated that to raise the temperature from 25C. to 37 C. required from 12-23 minutes.

Because of this length of time, the water bath has heretofore beenpreferred, even though the water bath presented considerable difliculty.Thus with a water bath, whenever the test tube was removed therefrom,both the test tube and the rack had to be wiped dry. Furthermore, thewater bath was bulky, required the frequent replacement of the water,and in itself required an undue length of time to bring to the desiredtemperature. Furthermore, as the water evaporated, there was a tendencyfor the solids to precipitate out, some of which would precipitate onthe sides of the test tubes which in time left a layer of scum thereonwhich would be difficult to remove. However, the water bath was muchfaster than the air bath and these difficulties were acceptable becauseof the fast heating time.

The present invention contemplates new and improved apparatus whichovercomes all of the above referred to objections and provides apparatuswhich has a minimum of bulk, does not require any liquids and heats thetubes and their contents almost as rapidly as a water bath.

In accordance with the present invention, a test tube heater is providedcomprised of a relatively thick block of metal in combination with meansfor heating the block to an elevated temperature and maintaining it atsuch temperature, one surface of the block having a plurality ofopenings of a predetermined diameter such as snugly to receive testtubes also of a predetermined diameter. By snugly receive, I intend tomean a diameter such that there will be a substantial area of metal toglass contact between the metal member and the sides of the test tubes.Thus the maximum diameter of the openings will be such as to receive alarge percentage, but not all, of a group of test tubes of a givenstated size when considering the normal manufacturing tolerances on r2,932,718 Patented Apr. 12, 1960 the diameters of such test tubes. Thebase of the openings may also be contoured to fit the shape of the lowerend of the test tubes.

Using the present invention it has been possible to heat specimens tothe desired temperature in a time period ranging from 55-133 seconds ascompared to a water bath which heats the specimens in a range of from60-72 seconds.

The principal object of the present invention is to provide a test tubeheater which is small in size, contains no liquids, is rapid in comingto its first temperature, is rapid in heating test tubes to the desiredtemperature and which is attractive in appearance.

A further object of the invention is the provision of a new and improvedtest tube heater having a plurality of openings to receive test tubes ofa diameter such as snugly to receive a large percentage of a stated sizetest tube whereby to provide a substantial area of metal to glasscontact.

Another object of the invention is the provision of a. new and improvedtest tube heater comprised of a metalblock having a plurality ofopenings therein to re-- ceive test tubes containing material to beheated, the: openings in the block being so dimensioned as to snuglyreceive the test tubes and provide a maximum rate of heat transferthereto.

Figure 2 is an end cross-sectional view taken approxi-- mately in line2-2 of Figure 3;

Figure 3 is a side cross-sectional view of Figure 2 taken approximatelyin the line 3-3 thereof, and

Figure 4 is a wiring diagram of the electrical circuit employed.

Referring now to the drawings wherein the showings are for the purposesof illustrating the preferred embodiment of the invention only and notfor the purposes of limiting same, the figures show a test tube heatercomprised of a metallic block 10 having in the upper surface thereof aplurality of vertically extending openings into each of which a testtube 12 is adapted to be inserted. The apparatus also includes a hollowbase 15 fastened to the underside of the block 10 by means of screws '16extending upwardly through an inturned flange 17 on the upper edge ofthe base 15. Legs or feet 18 fastened to the lower side of the base 15space same from the table top or wherever it is employed.

The base -15 as shown is generally hollow and provides a housing for thevarious electrical parts associated with the apparatus. Thus anelectrical heater unit 20 of conventional construction is fastened as byscrews 21 to the underside of the block 10 so as to be in thermalconductive relationship therewith. The heater 20 is preferably locatedsymmetrical on the lower surface of the member 10.

A heat operated switch or temperature sensing device 23 is inserteddirectly within the center of the metal block itself, among or betweentwo rows of tubes in an opening drilled orotherwise formed in the lowersurface of the member 10 and serves to energize or de-energize arelay 25mounted on the bottom of the housing 15. This relay 25 in turn hascontacts which serve to energize or de-energize the heater unit 20. Aswitch 26 and, a pilot light 27 are mounted on one side of the base 15for the purpose of controlling the,overall operation of the apparatus.

and several times greater than most other metals; the block provides aready reservoir of heat which can rejects only an occasional tube.

Electrical energy is supplied through a long flexible cord 28 whichenters the base 15 through an opening defined by an insulating collar29.

The switch 23 is connected so as to energize and. de-

energize the relay 25. When the relay is energized, its

contacts 30 are closed to in turn energizetthe heater.

provided which in the embodiment shown consist of a.v

dial type thermometer 33 which is actuated by thermally responsive meansin a stem 34 extending therefrom and inserted into a horizontal openinglongitudinally on the general centerline of the member 10. 1

It will thus be seen that a member has been provided for the purpose ofsupporting a plurality of test tubes in combination with means forheating and maintaining the member at a uniform elevated temperaturewhich temperature may be as desired depending upon the setting of thethermostat 23.

The member 10 may be of any desired heat conductive material, but in thepreferred embodiment is made of aluminum which in addition to its color,its ease of machinability and its resistance to corrosion,has a highheat conductivity, being second only to copper of the. readilyavailablecommercial metals. This thermal conductivity is several hundred times asgreat as that for water.

in addition to its thermal conductivity, the aluminum has ahigh thermalcapacity, almost twice that of iron Thus immediately flow'to a cold testtube 12 and when placed in one 011116 openings 11 commences to increaseits temperature. it is conducted rapidly through the block 10 fromotherportions thereof and from the heater. 20. Because of this high heatconductivity of the aluminum, the entire member 10 will reach andmaintain a substantially uniform temperature over all. r

The diameter of the hole 11 in relation to the diameters of the tubes 12forms an important part of the present invention. Thus, the diameter ofthe holes 11 should exceed the diameters of the tubes 12by the absoluteminimum amount. thickness layer of air space exists between 'the wallsof the openings 11 and the surfaces of the tubes 12 and infact"substantially the equivalent of a metal to glass contact over theentire surface of the tube '12 can be obtained. While the coetficient ofheat transfer of the tubes 12 will not be as large as it is with water,it is to be appreciated that because of the greater heat conductivity ofthe aluminum and because there are no'problems of stratas in water ofdifferent temperatures, the lower diameter of 10.065 millimeters and amedian diameter of 10.00 millimeters.v Over 50 percent of the tubes werewithin 1 percent (plus or minusOJ 'millimeter.)

of the stated diameter. For such tubes an opening diameter of 10.320millimeters was employed. This is equal to inch. Such a hole diameterprovides a' snug fit for most ten millimeter diameter test tubes and Itwill be appreciated for the fastest possible heatingrate of the contentsof the tube 12, the test tubes having the lower outer diameters shouldalso be discarded.

As heretofore indicated, a series of heating time tests As the heat isconducted to the tube 12,

By so ldoing,the minimum,

. v V 4 employing both a water bath, the present invention, and an airbath indicated that it is possible to obtain heating rates using thepresent invention in some cases faster than that of a water bath and insome cases only slightly slower. In all cases, howeverfthe heating rateis substantially faster than that with an air bath. Further, all of thedifficulties of the usual water bath, such as water evaporation,precipitation of solids and drippings are avoided.

The present invention has satisfied a very definite need in hospitals,maintaining blood banks and performing other typm of experimentaloperations wherein samples must be heated uniformly and quickly and. hasproven to be simplein construction and economical to manufacture.

Obviously modifications and alterations will occur to others uponreading and understanding this specifica tion and it is my intention toinclude allsuch modifications and alterations insofar as they comewithin the scope of the appended claims.

Having thus described my'invention, I claim:

' l. A test tube heater comprising a hollow base which" is open at itsupper end, a block of material having high heat conductivity and highheat capacity extending completely across the upper end of said base,said block having a plurality of rows of openings therein which are openat the top face of the block and extend downward therefrom and terminatein the block in closed lower ends which are spacedabove the bottom ofthe block,

temperature sensing means embedded in the bottom of the block, anelectrical heater member extending across the bottom of the block inheat conductive relationship therewith and projecting down from theblock into the interior of said hollow base, electrical control devicesfor said heater member mounted on said hollow base and having electricalconnections inside said base to said heater member, and a power cableleading into said base.

and having connections to saidcontrol devices.

2.'The heater of claim 1 wherein there is provided a heat sensitivemember extending lengthwise in said block between a pair of adjacentrows of said openings therein, and altemperature indicator connected tosaid heat sensitive member and positioned outside said block 'and saidbase.

- 3. A test tube heater comprising a block of material having high heatconductivity and high heat capacity, said block-having opposite side andend edges, side and end Walls depending from said edges of the block anddefining a hollow base, said block having a plurality of rows ofopenings therein which are open at the'top face of the block and extenddownward therefrom and terminate in the block inv closed'lower endswhich are .spaced above the bottom of the block, temperature sensingmeans in said block, an electrical heater member extending across thebottom of the block in heat conductive relationship therewith andprojecting down from the block into the interior of said hollow base,electrical control devices'for said heater member mounted inside saidhollow base and having electrical connections inside said base to saidheater member, and a power cable leading into said base and havingconnections inside thebase to said control devices.

References Cited in the file of this patent UNITED STATES PATENTS

